Fans are required in many technical fields in order to cool installations and systems and to keep the operating temperature thereof within the specified operating temperature range. In vehicles, fans are used for example in combination with a radiator in order to keep the vehicle engine within the specified operating temperature range for the engine and to prevent the engine from overheating.
If a fan of this type is used as a radiator fan in a motor vehicle, a vehicle control system usually presets a desired speed for the radiator fan in the fan control system. The fan control system then controls the radiator fan in a closed-loop manner in such a way that said radiator fan rotates at the predetermined desired speed. As a result, with constant ambient conditions, a constant air flow is generated or a constant air volume is conveyed by the radiator fan.
In such conventional fans, the air flow varies with changes in the ambient conditions. Ambient conditions such as temperature, height above sea level and the like are understood as changing ambient conditions, and these have an effect on the ambient air density.
If a motor vehicle is e.g. at high altitude, the air there is significantly thinner (i.e. less dense) than at sea level. As a result of this, however, the maximum air volume that the radiator fan can provide at the same speed is reduced. This can lead to the radiator fan not being able to provide enough air to cool the engine, even at maximum speed. Consequently, the temperature increases and an emergency operating mode of the radiator fan has to be activated, whereby the fan increases the speed up to an emergency speed. As an alternative, it would also be conceivable to over-dimension the radiator fan for such a case. This, however, would make the production of the radiator fan module as a whole both more difficult and more expensive.